Base-Specific Endo-Exonucleolytic Activity of Chlamydomonas Nuclease C1&2

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The reaction kinetics of nuclease C1&2 from Chlamydomonas reinhardtii were studied. It showed endo-exonucleolytic activity with sugar non-specificity. The relative rates of RNA breakdown were in order of poly(U) > poly(A) > yeast sRNA. In contrast, poly(G) and poly(C) released almost no acid_soluble materials after reacting with nuclease C1&2. The major products of a 100% limit digest of synthetic RNA homopolymers were mononucleotides with 3'-phosphate termini. Large oligonucleotides produced during endo-exonucleolytic degradation also appeared carrying 3'-phosphate termini. Nuclease C1&2 hydrolyzed single stranded DNA 20 times faster than double stranded DNA by endo-exonucleolytic action, releasing acid-soluble materials. High performance liquid chromatography of a 100% limit digest of salmon testes DNA demonstrated that the major products were deoxymononucleotides with phosphate at 3'-position. Furthermore, the level of 3'-dCMP among them was found to be extremely low. Poly(dC) and poly(me^5dC) were hydrolyzed much more slowly than single stranded (or denatured) DNA, releasing acid-soluble materials. The present results suggest that nuclease C1&2 is a base-specific nucleate 3'-oligonucleotidohydrolase different from the restriction enzymes.
日本植物生理学会の論文